1. Field of the Invention
The present invention relates to a method for producing ethyl 4-methyloctanoate, which is an aggregation pheromone substance of Coconut Rhinoceros Beetle (Oryctes rhinoceros), an insect pest of palm trees and others.
2. Description of the Related Art
Coconut Rhinoceros Beetle is an important insect pest of palm trees, pineapples, coconuts, sugarcane and others. It has markedly strong boring ability. The adults of this insect pest tunnel the shoot apex of such a plant and stay there with eating activity, so that the plant withers and dies at the time when the growing point was bored through by them and lost. This species is found over a wide area such as Southeast Asia, Hawaii, and Guam now. Although it brings enormous damage to plants belonging to the family Palmae, it cannot easily be controlled by insecticides and an effective control method has not yet been established. On the other hand, control with an aggregation pheromone substance has drawn attention and its use is expected.
It has been found that an aggregation pheromone substance of Coconut Rhinoceros Beetle is ethyl 4-methyloctanoate (R. H. Hallett et al., J. Chem. Ecol. 1995, 21(10), 1549-1570). Several synthesizing methods of this aggregation pheromone substance have been reported. For example, Gries et al. have reported that ethyl 4-methyloctanoate can be obtained by reacting a Grignard reagent prepared from magnesium and 2-chlorohexane with ethyl acrylate in the presence of tetrahydrofuran, hexamethylphosphoric triamide, trimethylchlorosilane and, as a catalyst, copper (I) cyanide (G. Gries et al., Z. Naturforsch. 1994, 49c, 363-366). Valentine et al. have also reported that ethyl 4-methyloctanoate can be obtained by successively carrying out the following four steps of: a Mannich reaction between 1-hexanal and a 37% aqueous formalin solution, a reduction reaction of the aldehyde, a Johnson-Claisen rearrangement reaction, and a hydrogenation reaction (Valentine et al., J. Agricultural and Food Chemistry. 2007, 55, 5050-5052).